IBM 3270 PC/GX Capacitor Replacement Guide
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The IBM 3270 PC/GX is an IBM 5371 system unit, the same type as the IBM 3270 PC/G, driving a 19-inch IBM 5379 Display through an IBM 5378 Display Attachment Unit. IBM states that the 5371 is based on a 5160 System Unit for the PC XT, that the 3270 PC, G and GX system board settings are the same as for the 5160, and that all base system parts for the 3270 XT products are the same as 5160 XT base system parts.[1]
The system unit's capacitor work is PC XT work, covered on the IBM PC XT Capacitor Replacement Guide: sixteen tantalums on the system board, thirteen of them on +5 V; C55 (ceramic) and C56 (tantalum) on +12 V; 10 µF 16 V (or higher voltage) as the replacement.[2][3][4] The 5371's own adapter cards are listed on the IBM 3270 PC/G Capacitor Replacement Guide. Unlike the PC/G's 5278 and 5279, the 5378 and 5379 are documented to card level, because IBM's AT/GX maintenance manual covers the same two units.[5]
Power arrangement
[edit | edit source]On the PC/GX the mains enters through the 5378, which feeds the 5379. This is the reverse of the PC/G, where the display feeds the attachment unit. IBM: the 5379 "receives power from the 5378 Display Attachment Unit", and "the 5378 has a 1.8-m (6-ft) power cable and requires its own power source."[1] The On/Off switch on the front of the 5378 controls the mains to the 5379.[5]
| Unit | Mains | Fed from |
|---|---|---|
| 5371 system unit | Own power cord | |
| 5378 Display Attachment Unit | Own power cord, 1.8 m | |
| 5379 Display | None | The 5378 |
A dark 5379 with the 5378 switched off is normal.[5]
Safety
[edit | edit source]- The 5379 carries an IBM hazard label reading 25000 V (P/N 4421680) and has a rear safety shield (P/N 4421919 monochrome, 4421918 colour).[5] Follow the CRT Discharge Procedure.
- IBM's CRT instructions: some CRTs build up a second capacitive charge after the first discharge, so discharge each tube a second time immediately before removal. Wear safety glasses (IBM P/N 5715010) and a long-sleeved garment, and do not handle a CRT by the neck alone.[5]
- The 5378 carries an IBM hazard label reading 800 V (P/N 4421640).[5] Discharge its supply through a resistor and confirm with a meter before touching the boards.
- The 5378 mains fuse is 6 A slow-blow 250 V (P/N 5214456).[1][5]
IBM 5378 Display Attachment Unit
[edit | edit source]The 5378 contains a Motorola 68000 graphics processor with 128 KB of memory shared with the system unit.[1] It connects to the system unit by a 62-way bus extender cable and to the 5379 by 2 m cables.[5][1]
Supply rails
[edit | edit source]The 5378 supply provides +5 V, −5.2 V, +12 V and −12 V.[5] IBM's checks:[5]
- Look at the four LEDs on top of the power supply. All four should be lit.
- Measure +12 V at the fan connector: 10.8 to 13.2 V.
- Measure +5 V at the logic boards (A1-D2D03 and B1-A2D03): 4.8 to 5.2 V. Measure −5.2 V at B1-A2D06: −4.9 to −5.5 V.
| Voltage | P3 pins |
|---|---|
| +5 V | 1, 2, 3, 4 |
| +5 V sense | 5 |
| +12 V | 6 |
| −12 V | 9 |
| −5.2 V | 10, 13 |
| Return | 7, 8, 11, 12, 14 |
If the 5378 supply will not come up, check the voltage selector switch at the upper right of the rear of the supply before anything else. IBM's note says the switch shows the voltage it is set for, 115 for the USA and Canada.[1]
The 5378's mains fuse also carries the 5379. If a new fuse blows again, IBM's table DAU24 has you unplug the 5379's mains cable from J2 on the rear of the 5378 and fit another fuse. If that one holds, the short is in the cable or in the 5379's primary power supply assembly; if it still blows, the fault is in the 5378 supply. With only some of the four LEDs lit, unseat the cards in turn to find one that is shorting the supply.[6]
Parts
[edit | edit source]| Part | IBM number |
|---|---|
| Power supply assembly | 4421613 |
| Fuse, 6 A slow-blow, 250 V (in the supply) | 5214456 |
| Fan, 12 V (two fitted) | 4421586 in the Service Information Manual, 4421916 in the AT/GX manual |
| Fan shockmount (four) | 4421589 |
| Logic boards A and B | 8223695 and 8223696 |
| Logic board, support | 4134800 |
| Interconnect card | 8233876 |
| Logic gate | 4421583 (SIM), 4421585 (AT/GX manual) |
| Cable assembly, video | 4421620 |
| Cable assembly, signal flexi | 8233832 |
| Cable, 5371 attach | 8529253 |
| Label, hazard 800 V | 4421640 |
| Card | Location | IBM number |
|---|---|---|
| Update control | A1-A2 | 8223584 |
| System control | A1-B2 | 8223717 |
| Graphics processor | A1-C2 | 6243723 |
| Display bus receiver | A1-D2 | 8233700 |
| Clock and video driver | B1-A2 | 8223671 |
| Bit plane 4/5 | B1-B2 | 5147884 |
| Bit plane 2/3 | B1-C2 | 5147884 |
| Bit plane 0/1 (colour Model C01 only) | B1-D2 | 5147884 |
The supply is a single assembly. Neither manual lists a capacitor, rectifier or regulator in it separately, and neither includes a schematic.[1][5]
IBM warns that the 5378 logic boards can be inserted wrongly, which damages cards. Fit each board with the angled corner of its land pattern farthest from the fan and towards the top of the housing; the A1 board has that corner towards the bottom.[1] IBM's mnemonic for the card pin letters in each row (D, J, P, U, B, G, M, S) is "Dow Jones Prices Up Buy General Motors Stock".[1]
IBM 5379 Display
[edit | edit source]IBM breaks the 5379 down to individual cards:[1][5]
| Part | Monochrome (M01) | Colour (C01) |
|---|---|---|
| Card, power supply | 4421761 | 4421621 |
| Power supply assembly, primary | 4421765 | 4421626 |
| Card, video amplifier | 4421763 | 4421623 |
| Card, deflection amplifier | 4421762 | 4421622 |
| Card, CRT socket | 4421766 | 4421707 |
| Card, manual controls | 4421764 | 4421625 |
| CRT and bezel assembly | 4421768 | 4421767 |
| Degauss coil assembly | 4421631 | |
| EHT cable | 4421632 | 4421632 |
| CRT ground wire | 4421917 | 4421917 |
| Fan | 4421624 | |
| Fan, rubber mount | 4421630 | 4421630 |
| Cable, twin-ax assembly | 4421629 (two) | 4421629 (four) |
| Safety shield, rear | 4421919 | 4421918 |
| Label, hazard 25000 V | 4421680 | 4421680 |
The power supply is in two parts, a primary power supply assembly and a power supply card, each a separate FRU. IBM lists separate Northern and Southern Hemisphere versions of the colour display and of its CRT and bezel assembly, with a list of countries for each.[5] No capacitance values are published for any 5379 card.
IBM's capacitor note: CRT card arcing
[edit | edit source]IBM's diagnostic tips include one capacitor fault on the 5379: an out-of-focus or unstable picture caused by high-voltage arcing across two capacitors on the CRT card, the two mounted on the side of the card that faces away from the tube. IBM promised a corrected card; its temporary fix was to separate the two capacitors from each other as far as physically possible.[1] Look there first on a 5379 with poor focus or an unstable picture.
ECA037: deflection card connector
[edit | edit source]A separate tip concerns the colour deflection amplifier card, P/N 4421622. The XY connector from the yoke changed from serial number 2585, from green to brown, and the old and new parts do not mate. IBM's CRT/adapter kit P/N 59X6942, under ECA037 (1 November 1988, service code 33), corrects it when a replacement CRT/yoke assembly or deflection card does not match.[1] The procedure:[1]
- Select the correct adapter from the kit.
- Cut the mismatching plug off the CRT/yoke assembly within 50 mm (2 in) of where the green and yellow wires enter the plug housing.
- Strip 6 mm (0.25 in) from the existing and replacement wires, join green to green and yellow to yellow in the in-line crimps with no bare conductor showing, and compress them with tool P/N 450898.
- Plug the XV connector into the XV socket on the deflection amplifier card. On a male XV plug the upper wire is yellow and the lower green; on a female plug the upper wire is green and the lower yellow.
5379 reference figures
[edit | edit source]Figures to judge a 5379 against:[1]
- 19-inch screen, viewing area 280 × 280 mm.
- 1024 × 1024 pels, 93 pels per inch, in the graphics layer; 80 × 50 characters in a 12 × 20 box in the text layer.
- 52 frames per second non-interlaced (the AT/GX manual gives 57).[5]
- Colour: up to 16 colours in the graphics layer, 8 in the text layer. Monochrome: four intensities in graphics, two in text.
- 100 to 127 V, 50 or 60 Hz, supplied from the 5378.
- Weight 35 kg (77 lb); tilt −5 to +15°, swivel ±120°.
The 5378 is 495 × 406 × 130 mm and 14 kg.[1]
Things that are not faults
[edit | edit source]- A blank 5379 when only the 5378 and 5379 are powered up without the 5371: IBM notes that no test pattern appears in that case.[1]
- A dark display with the 5378 switched off.[5]
- Interference between a 5379 and a second-screen 5151 placed close together, or with a printer or plotter less than 305 mm away.[1]
When to recap
[edit | edit source]On the system unit, follow the IBM PC XT Capacitor Replacement Guide. On the 5378 and 5379, with no published component values:
- replace a capacitor that is visibly bulging, leaking, cracked or burnt;
- check the rails against IBM's limits above before suspecting capacitors, and check the CRT card capacitors first on a 5379 with poor focus;
- replace line suppression capacitors that crack or smell with parts of the same safety class.[7]
Read each value from the part itself or from the same position on a donor card.
Related pages
[edit | edit source]- IBM 3270 PC/GX
- IBM 3270 PC/GX Maintenance Guide
- IBM 3270 PC/GX Troubleshooting Guide
- IBM PC XT Capacitor Replacement Guide
- IBM 3270 PC/G Capacitor Replacement Guide
- Capacitor Failure Symptoms
- CRT Discharge Procedure
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, 1989, hosted as IBM Personal Computer Family Service Information Manual. Chapter 10, pp. 10-5 to 10-13 (PC/GX description, 5378 and 5379 specifications and power, 5378 card plugging chart and pin locator, diagnostic tips for the 5378 and 5379, 3270 unique error codes); chapter 18, assemblies 22 and 23, pp. 18-38 to 18-41 (5378 and 5379 parts); chapter 19, ECA037.
- ↑ minuszerodegrees.net, "Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard" (5150_5160/MDC/tantalum_short_plus_5volts.htm).
- ↑ minuszerodegrees.net, "Short-circuit on the +12 volt line of an IBM 5150/5155/5160 motherboard" (5150_5160/MDC/tantalum_short_plus_12volts.htm).
- ↑ minuszerodegrees.net, "IBM 51xx motherboards/cards - types that are wired to use 2-legged tantalum capacitors" (failure/). 10 µF at 16 V or higher.
- ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 5.16 IBM, IBM 3270 Personal Computer AT/GX Maintenance Information, SY33-0125-1, June 1986, hosted as IBM 3270 PC AT/GX Maintenance Information. CRT handling pp. xliv-xlv; 5378 description p. 1-12; power-off sequence p. 1-17; 5378 card locations p. 3-4400-1; 5378 power supply tables DAU23 to DAU25, pp. 3-4400-39 to 3-4400-41; parts catalogue pp. 7-6, 7-7, 7-10 and 7-12.
- ↑ IBM, IBM 3270 Personal Computer AT/GX Maintenance Information, SY33-0125-1, table DAU24, pp. 3-4400-40 and 3-4400-41.
- ↑ minuszerodegrees.net, "Commonly Failing Electronic Components (in vintage computers)" (failure/failure.htm). Line suppression capacitors and their replacement rules.